In an image capturing apparatus such as a digital camera, a foreign substance such as dust or mote (to be simply referred to as dust hereinafter) sometimes adheres to the surface of an image sensor protective glass fixed to an image sensor, the surface of an optical element placed in front of the image sensor, or an optical system (which will be generically referred to as an image sensor optical component hereinafter). When dust adheres to an image sensor optical component, the dust blocks light, an image at the light-blocked portion is not shot, and the quality of the shot image degrades.
In cameras using silver-halide films as well as digital cameras, dust on a film is also captured in an image. However, the film moves frame by frame, and hence dust is very rarely captured on all frames.
In contrast, the image sensor of the digital camera does not move, and one image sensor shoots an image. Once dust adheres to an image sensor optical component, the dust is captured on many frames (shot images). In particular, a lens-interchangeable digital camera has a problem that dust tends to enter the camera at the time of lens interchange.
The user of the camera therefore must always care about the adhesion of dust to an image sensor optical component, and spends much effort to check and clean dust. Since an image sensor, in particular, is placed relatively deep inside the camera, it is not easy to clean or check dust.
Dust enters a lens-interchangeable digital camera when attaching or detaching a lens. Furthermore, dust easily adheres to an image sensor optical component owing to wear or the like upon driving of a focal plane shutter placed immediately before an image sensor.
Since such dust on the image sensor generally adheres onto a protective glass or optical element instead of the surface of the image sensor, the dust is imaged in different states depending on the aperture value or pupil position of a photographing lens. That is, as the aperture value approaches the open F-number, a shot image blurs, and hence even the adhesion of small dust has almost no influence on the image. In contrast, as the aperture value increases, such dust is clearly imaged, and hence affects the image.
To solve this problem, there is known a method of making dust less noticeable. According to this method, an image of only dust on an image sensor is prepared in advance by shooting a white wall or the like while setting the lens at a large aperture value. This image is used in combination with a general shot image (see Japanese Patent Laid-Open No. 2004-222231).
There is also proposed a technique of vibrating an image sensor optical component to shake off dust adhering to it (see Japanese Patent Laid-Open No. 2002-204379).
It is possible to combine a method of detecting the position of dust on an image sensor to obtain dust correction data in order to correct a shot image portion, and correcting shot image data, as disclosed in Japanese Patent Laid-Open No. 2004-222231, and a method of shaking off dust, as disclosed in Japanese Patent Laid-Open No. 2002-204379. This technique can increase the correction precision because after dust is shaken off and reduced, shot image data containing the dust image is corrected.
However, if dust is shaken off after obtaining dust correction data, a dust adhesion state after shaking off dust does not match dust correction data.
In an image capturing apparatus capable of using an interchangeable lens, dust may newly adhere to the lens at the time of lens interchange. Also in this case, the dust adhesion state does not match dust correction data.